By Martha McHardy

An infectious diseases expert has warned that the US could see a syndemic — where more than three pathogens are causing outbreaks at once — as respiratory illness cases soar across the US.

Dr Raj Rajnarayanan, an infectious diseases expert in Arkansas who tracks Covid variants, warned a new wave of infectious diseases is emerging and it could hit children and the elderly the hardest this winter.

More than a dozen states have seen a surge in respiratory illness cases in recent months, including flu, Covid-19, and respiratory syncytial virus (RSV), with rates of infections either “high” or “very high,” according to the Centers for Disease Control and Prevention.

The CDC said 15 states are experiencing a surge in infectious diseases, with South Carolina and Louisiana experiencing “very high” rates of infection, while Alabama, California, Florida, Texas and New Jersey have been deemed to have “high” levels of respiratory illnesses.

New York City is also experiencing “high” levels of respiratory illnesses, the CDC said. However, New York state has “low” levels overall.

CDC Director Dr Mandy Cohen said Americans in affected states should consider wearing a face mask over the holiday season to protect themselves and others from respiratory illnesses. She also advised people to get their latest Covid, flu and RSV vaccines.

“Use additional layers of protection like avoiding people who are sick, washing your hands, improving ventilation and — wearing a mask,” Dr Cohen said.

Nationwide, cases of respiratory illness are higher than pre-pandemic levels, with Covid and flu cases on the rise.

The week ending 2 December saw 11.5 per cent of Covid tests come back positive, while 6.8 per cent of flu tests were positive – an increase from 10.6 per cent and 6.2 per cent, respectively, from the week ending 25 November.

The rate of RSV infections has fallen from 12.8 per cent to 11.8 per cent in the same period.

Meanwhile, emergency department visits for RSV, Covid and flu have doubled since late October. Around half of hospital visits were attributed to Covid, with 22,500 hospitalizations in the week ending 2 December, while the rest were due to flu and RSV.

While rates of hospitalisation for flu were comparable in the same period in 2019 – the last cold season before Covid emerged – this year’s cold season began in October, the CDC said, a month earlier than usual.

It comes after the CDC said it was tracking a new Covid variant – JN.1 – which is believed the be the cause of 15 to 29 per cent of Covid cases in the US as of 8 December.

The new variant was first detected in the US In September. In October, it accounted for just 0.1 per cent of Covid cases nationwide, but cases have seen a huge surge since then.

Due to its rapid spread, the CDC believes it is either more transmissible or better at evading the human immune system, but there is no evidence the variant poses an increased risk to people and no indication it is more severe than previous variants.

Separately, Ohio and Massachusetts have seen an outbreak of pediatric pneumonia, dubbed “white lung syndrome”, that has infected children in Denmark and China, with the average patient being around eight years old.